CANCUN, Mexico – Mexican federal police have arrested the mayor of the resort city of Cancun on drug trafficking, money laundering and organized crime charges, a new blow to an election season already marred by violence and allegations of drug cartel involvement.

Gregorio Sanchez, who took a leave of absence from the Cancun mayoral post to run for governor of the Caribbean coastal state of Quintana Roo, was taken into custody Tuesday at Cancun’s international airport after arriving on a flight from Mexico City.

The federal Attorney General’s Office said Sanchez is suspected of offering information and protection to the Zetas drug gang and the Beltran Leyva cartel, which are active in Quintana Roo.

Officials said they could not immediately recall another case in which a gubernatorial candidate had been arrested on drug charges.

“This takes us all by surprise, it is unprecedented,” said state Gov. Felix Gonzalez Cantu.

Ricardo Najera, a spokesman for the federal Attorney General’s Office, said Wednesday that Sanchez is accused of fomenting or aiding drug trafficking, engaging in organized crime and making transactions with illicitly obtained funds.

Sanchez’s Democratic Revolutionary Party denounced the charges as politically motivated.

“This is a crass ploy, a trickery to stop Gregorio from becoming governor of the state, stop him at all cost,” the leftist party’s national leader Jesus Ortega said in an interview Wednesday with MVS Radio.

Ortega likened Sanchez’s arrest to last year’s stunning round up of 12 mayors in the western state of Michoacan for alleged ties to a drug cartel just two months before congressional elections. All but two have since been released for lack of evidence, fueling allegations that the arrests were politically motivated. Michoacan is a Democratic Revolution stronghold, though some of the arrested mayors were from other parties.

A Twitter account linked to Sanchez’s website vowed to continue Sanchez’s campaign and asked people to protest his arrest and vote for him.

Najera denied there was any political motivation behind Sanchez’s arrest. He said the evidence includes several protected witnesses and documents from the Finance Department’s investigative unit that indicated the mayor was leaving well beyond his means.

Observers have voiced fears that Mexico’s drug cartels could seek to infiltrate politics and control the July 4 elections in 10 states by supporting candidates who cooperate with organized crime and killing or intimidating those who don’t

On May 13, gunmen killed Jose Guajardo Varela, a candidate for mayor of Valle Hermosa, a town in the border state of Tamaulipas that has been ravaged by drug violence. The leader of Guajardo Varela’s conservative National Action Party said the candidate had received threats telling him to quit the race.

Sanchez’s website quoted him as saying he had been threatened. “Resign from the race, or we are going to put you in jail or kill you,” Sanchez said in describing one of the threats.

Sanchez, a populist who pledged to bring services to the impoverished majority of residents who live on the outskirts of the glittering resort, took on the entrenched political machine of the Institutional Revolutionary Party that has long controlled Quintana Roo.

Velasco already had been detained for questioning in the killing of retired Brig. Gen. Mauro Enrique Tello, whose bullet-riddled body was found in a car in early 2009, shortly after the Cancun city government hired him as a security consultant to combat local corruption.

Earlier this month, Mexico extradited former Quintana Roo Gov. Mario Villanueva to the U.S. to face charges of conspiring to ship hundreds of tons of cocaine and to launder millions of dollars in bribe payments through Lehman Brothers in New York and other financial institutions. Villanueva had been arrested in 2001.

Bundles of cocaine sometimes wash ashore in the region because smugglers drop drugs from boats or small planes for gangs to retrieve and move into the United States.